Excessive emission of carbon dioxide caused by the combustion of fossil fuels has been considered as the primary cause of global warming, about ⅓ of which is from power plants emission. Thus the separation and capture of the carbon dioxide from power plants has become a priority in emission reduction all over the world. At present, there are three leading approaches for separating carbon dioxide, i.e., pre-combustion capture, post-combustion capture, and oxygen-rich combustion capture. The pre-combustion capture has been considered to be a promising approach for decarbonization, and IGCC (Integrated Gasification Combined Cycle) process is considered to be an effective approach for pre-combustion capture.
The synthetic gas produced by IGCC process is a mixture of carbon dioxide and hydrogen wherein the carbon dioxide accounts for 20%-40% of the mixture, and has an outlet pressure of 2-5 MPa. By removing the carbon dioxide within it, the IGCC synthetic gas only produces water as combustion product which does no harm to the environment, making it a clean energy. Thus, the separation and capture of carbon dioxide has become the key of the technology.
At present, methods for separating and capturing carbon dioxide in IGCC synthetic gas mainly include cryogenic separation process, chemical absorption process, membrane absorption process, and combined physical and chemical absorption process. Chen has made a research on the chemical absorption process and presented a systematic evaluation (Study on CO2 Capture Technology Based on IGCC Power Generation Systems, 2014). Zhang has presented a systematic review on the current carbon dioxide capture processes, focusing on the influence of the adsorbent on the adsorption of carbon dioxide (Adsorptive Separation of Carbon Dioxide, 2012). The above mention methods have been proofed to be efficient in practice, but problems exist, such as high operating cost, secondary pollution, and the underdevelopment of supporting technologies. Li et al has disclosed a hydrate-based process for separating carbon dioxide which is considered to be low-cost and non-pollution (Chinese patent publication No. CN103638800A). Song et al has disclosed an apparatus for the hydrate-based separation (Chinese patent publication No. CN103961989A). Compared with the traditional methods, apparatuses for separating and capturing carbon dioxide using hydrate-based method present advantages, but challenges in commercialization exist such as low hydrate formation rate, and incapability of continuous production; furthermore, while the efficiency of primary separation is low, multi-stage separation has a challenge in commercialization that, as the concentration of the carbon dioxide is reduced in each stage, the required pressure for hydrate formation will rise dramatically in the subsequent stage.